topic 4 : river processes

topic 4: the uk's evolving physical landscape

freeze thaw

when rainwater enters gaps in rocks and freezes, the ice puts pressure on the rock and causes it to break

acid rain

rain containing high amounts of chemical pollutants such as nitric and sulfuric acids, which when it falls can react with the minerals in the ground and cause dissolving and decay.

biological weathering

when the roots of plants grow into cracks of gaps and pushes the rock apart

soil creep

individual particles of soil move slowly down a slope due to gravity

slumping

when the bottom of a valley side is eroded, the slope becomes steeper and the material slides downwards

hydraulic action

sheer force of water hitting the river bed and banks, wearing them away

abrasion

material scraping or rubbing along the banks and bed of the river

solution

river water is slightly acidic so can dissolve some rocks and minerals

attrition

particles in the river bashing into each other, wearing each other down and becoming smaller and rounder

traction

stones rolling along the river bed

saltation

smaller particles bouncing along the river bed

suspension

the water flow carries silt and sand particles

erosion

the breaking away and removal of materials by a moving force e.g. river, wave, glacier

four types of erosion?

hydraulic action, abrasion, attrition & solution

weathering

the breakdown & decay of rock by natural processes acting on rocks, cliffs & valley sides

three types of weathering?

physical, chemical, biological

mass movement

the movement of material down a slope due to gravity

four types of mass movement?

falls, slumps/slides, creeps and flows

mudflow

saturated soil flows down a slope

landslide

large blocks of rock slide downhill

rockfall

bits of rock fall off the cliff face, usually due to freeze-thaw weathering

transportation

the carrying of sediment downstream from the point where it has been eroded to where it is deposited

four types of transportation?

solution, suspension, saltation, traction

deposition

when a river loses energy it drops/deposits the sediment it has been carrying

freeze-thaw weathering

1. water enters cracks in the rock.

2. when air temperature drops below freezing, the water will freeze and expand by 9-10 percent putting pressure on the rock

3. the ice will melt and contract when the temperature rises above freezing

what happens if the process of freeze thaw weathering is repeated?

the rock will weaken and eventually shatter into angular fragments - the fragments may then be deposited as scree at the foot of a slope

onion skin weathering/exfoliation

when a rock's outer layer peels off due to extreme variations in temperatures

describe what happens with different temperatures in exfoliation

when temperature is high, the rocks expand e.g in desert areas, when temperature drops during the night, the rocks contract

describe how river processes of erosion, transportation and deposition change downstream (8 marks)

"You need to start at the upper course, then talk about the middle and lower course. Don't forgot to mention deposition. You must use correct terms."

what is the upper course like?

• narrow/shallow channel

• high bedload

• steep/v-shaped valley

what is the middle course like?

• open/gentle sloping valley with floodplain

• wider/deeper channel

• more suspended sediment

what is the lower course like?

• open/gentle sloping valley with floodplain

• flat and wide floodplain

• very wide and deep channel

upper course features

• interlocking spurs

• gorges

• waterfalls

• ‘v’ shaped valleys

middle course features

• meanders

• river cliffs

• slip off slopes

lower course features

• ox-bow lakes

• floodplains

• levees

why certain fluvial processes occur at different places along the river?

modal answer:
firstly, deposition processes predominantly occur in the lower course, e.g by the mouth of the river, this is because the river is moving slowly and will lose energy, causing it to drop sediment.

secondly, vertical erosion ocurs mainly in the upper course, for example by a waterfall - shown in the figure, this is because the water is travelling down a steep gradient and therefore erode downwards.